1. Field of the Invention
This invention relates to collapsible strut constructions, and more particularly to such constructions wherein telescoping strut members are lockable in extended positions.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
The following prior art references are hereby cited as being of interest.
U.S. Pat. Nos.:
______________________________________ 3,367,689 3,390,874 3,442,541 3,469,871 4,014,467 4,362,415 4,366,945 4,453,449 4,453,728 4,546,956 4,682,795 4,960,344 5,066,049 ______________________________________
U.S. Pat. No. 3,442,541, FIG. 1, discloses a releasable fastener in the form of a strut having telescoping inner and outer members, and a locking sleeve which is slidable on the outer member and which controls movement of locking dogs carried respectively in radial slots in the outer member. The inner member has a series of transverse locking ribs which are engaged by corresponding locking ribs on the dogs. With the locking sleeve in its locked position, the dogs are in forcible locking engagement with the ribs on the inner member. When it is desired to release the strut, the sleeve is shifted axially to a position wherein the locking dogs can shift outwardly in response to axial force applied between the telescoping members, and the latter can thereafter collapse into one another, as desired.
U.S. Pat. No. 3,469,871 illustrates a lockable coupling having telescoping inner and outer members and which employs two arcuate locking dogs carried in a circumferential groove of the inner member, and also employs multiple force-transmitting balls housed in radial slots of the inner member. Each arcuate locking dog is engaged by two balls. In operation, a release member or rod having a conical actuator portion engages the balls and shifts them radially, along with the arcuate locking dogs. During locking, the dogs are shifted laterally into inner annular grooves on the outer telescoping member. Locking and release of the telescoping members is accomplished by axially displacing the release member, via a pin-coupled release collar (64, FIG. 2) carried by the inner telescoping member.
Other constructions involving struts of the type employing radially shiftable locking components are illustrated in U.S. Pat. No. 3,390,874 and U.S. Pat. No. 3,367,689.
U.S. Pat. No. 4,362,415 illustrates a locking strut having a slidable locking collar which can be positively retained in a locking position by an external spring-biased locking lever.
Less pertinent is U.S. Pat. No. 4,546,956, which discloses a releasable coupling for a hose attachable to a supply of compressed gas. The arrangement is such that the coupling cannot be removed from the supply fitting until after the pressure is reduced, to minimize danger to personnel from an inadvertent, gas-propelled "fly off" of the coupling. Although this device provides a safety interlock feature, it is not a strut, and the structure and mode of operation of the device is different from that of the invention, as will be apparent hereinbelow.
U.S. Pat. Nos. 4,014,467; 4,366,945; 4,453,748; 4,682,795; and 5,066,049 all involve releasable hose fittings/-couplings having various types of locking structures that employ captive balls.
U.S. Pat. No. 4,960,344 discloses a coupling between a drive shaft and a driven shaft. U.S. Pat. No. 4,453,449 relates to a re-useable, non-destructive hold-down apparatus employing locking balls, which apparatus grips a member such as a missle or projectile, until a certain tension is developed by the same, and which thereafter releases the member suddenly.
In connection with those of the above patents dealing with struts, there existed significant problems involving inadvertent release under load. Specifically, with either compressive or tensile loads applied between the telescoping members of the prior art struts, there was a danger that the operator could slide the locking collar (or other release mechanism) to a release position while the strut was still under load, possibly leading to a sudden collapse of the strut and an accompanying uncontrollable swing or fall of the member being held, by virtue of its own weight. Such a condition was capable of causing serious injury to either the operator or to other personnel in the area.
In the past, struts of the type noted have been used with aircraft cowlings, in order to retain the cowlings in an open position as during maintenance and/or servicing of the aircraft engines. Depending on the size of the aircraft, such cowlings can weigh many hundreds of pounds, and the potential of injury resulting from being struck by an inadvertently released cowling can be readily appreciated if one considers structures of such magnitude and size.